Project Abstract Climate change is expected to impact the human exposure to multiple environmental stressors (e.g. heat waves, air pollution, forest fires). Studies to date have largely examined these environmental stressors individually and currently we don't have the much needed research framework to do otherwise. To better understand how climate change will directly and indirectly alter human health risks and to identify those who will be most vulnerable to adverse health effects, we need to develop a new research framework that addresses the following challenges: 1) adaptation: the capacity of individuals and their communities to adapt to heat will affect the extent to which climate change will impact morbidity and mortality; 2) climate induced changes in atmospheric system: ambient air pollution levels will change in response to the altered meteorological conditions arising from climate change; 3) health risks of multiple exposures: the health effects of combined exposure to degraded air quality and heat could be more severe than would be expected based on the individual exposures (i.e., synergism). Our main objective is to develop an innovative research framework that will link national databases on health to atmospheric conditions under a changing climate. We plan to: 1) characterize future adaptation to extreme heat (Aim 1); 2) project future exposure to both extreme heat and air pollution (Aim 2); and 3) estimate future health risks associated with joint exposure to heat and air pollution under a changing climate accounting for adaptation (Aim 3). To mitigate the public health consequences of climate change we need to recognize the synergy due to concurrent changes in several environmental stressors and that populations will adapt. This is the first national study that will characterize the public health consequences of concurrent changes in exposure to heat and air pollution under changing climate. By strengthening our understanding of which communities and populations will be most vulnerable and of how they will adapt, we will greatly impact the development of environmental interventions and adaptive strategies.